Method for processing mineral fibers



p 1953 H. w. ESSMAN 2,653,355

METHOD FOR PROCESSING MINERAL FIBERS Filed Aug. 50 1950 V INVENTOR:.ZZIIZZULD- Wfissmzxz.

Patented Sept. 29, 1953 METHOD FOR PROCESSING MINERAL FIBERS Harold W.Essman, Newark, Ohio, assignor to Owens-Corning Fiberglas Corporation, acorporation of Delaware Application August 30, 1950, Serial No. 182,340

14 Claims.

This invention relates to a method and apparatus for treating orconditioning linear groups or strands of mineral fibers and moreespecially to a method and apparatus for conditioning and severingstrands of glass fibers suitable for particular uses where control ofstrand and fiber orientation is essential.

It has been a practice to process strands of continuous mineral fibers,as for example attenuated glass fibers, to produce masses of shortlength strands and individual fibers which are especially adaptable forforming fibrous mats and particularly predetermined shapes termedpreforms usable as reinforcing mediums in molded plastic or resinousarticles. Such masses of short strands of continuous fibers areespecially desirable as the multifiber strand or yarn possesses greatstrength with a minimum of weight or quantity of material used. Suchmasses of short length strands and fibers are extremely fiexible and areadmirably suited as reinforcing means for articles of varying contoursas they may be readily shaped to any desired configuration.

A strand or yarn formed of comparatively fine attenuated glass fibersusable for the purposes mentioned contains upward of two hundred or morecontinuous fibers which are usually held in strand or yarn formationthrough the application of an adhesive or bonding material such asstarch, gelatin or other bonding agent. After the strands or yarns aresevered or reduced to short lengths, the adhesive or bonding materialholds the fibers in strand form. For most satisfactory results it isdesirable that some of the severed strands be opened up or disintegratedto result in separated or individual fibers and strands containing fewerfibers.

The various uses for short length strands or fibers require differentratios of intact strands, partially opened strands and individual fibersdepending upon the particular use for the fibrous material. If a densemat or fibrous mixture is desired, it should contain a high percentageof unopened or partially opened strands with comparatively fewindividual fibers. If a relative ly light weight, fiuffy, resilient massis to be had, the amount of individual or separated fibers predominatein the collected fibrous mass. The strength factorof the mass may bevaried by modifying the ratio of intact strands to subdivided strandsand individual fibers or zones of different strength characteristics setup by varying the ratio during collection of the strands and fibers toform a mass,

Heretofore a difficult problem has been pre sented to obtain desiredmixtures of cut strands and fibers and control the ratio of unopenedstrands to subdivided strands and separated fibers. One method that hasbeen employed involves collecting an adhesive bearing strand of glassfibers by winding same in spool or package form, splitting the strandpackage lengthwise, and feeding the mass of strands to a spiral cuttingdevice or chopping machine to form short length strands. The severedstrands formed in this manner are not of uniform length because thestrand mass fed to the spiral cutter is not susceptible of precisioncontrol of the severed strand lengths.

Another factor affecting the character of the collected mass of severedstrands is the condition of fixation. or set of the adhesive or binder.If the binder is substantially set or hardened, the fibers of thesevered strand are integrated or strongly boinid together so that theresulting collected mass is composed of substantially intact or unopenedfibers. If the binder is not completely hardened, then the severedstrands tend to adhere together in tangled clumps or groups, a conditionwhich renders the collected mass wholly unsuitable for most purposes.

In an endeavor to surmount these difficulties, the mass of severedstrands and tangled clumps or groups of strands are subjected to aseries of mechanical picking devices to separate tangled clumps orgroups of severed strands and to open up some of the strands to smallerstrands and individual fibers. This method is incapable of accuratecontrol and is inadequate to attain a collected mass of severed strandsor fibers of predetermined character or to selectively obtain individualstrands, partially opened strands or those having fewer fibers,individual or separated fibers or various combinations thereof.Furthermore, such method is not well adapted for collocating the typesof fibers during assembly so as to orient the unopened or partiallyopened strands interiorly of a preform for desired strengthcharacteristics with surface areas predominating in separated orindividual fibers.

The present invention embraces the provision of a method of treatingcontinuous strands of adhesive-bearing mineral fibers in a manner toestablish uniform fixation of the adhesive complement of the strands toenable the establishment of better control of the character of acollected mass of individual fibers and groups of fibers formed fromcontinuous strands or yarns.

An object of the invention is the provision of a simple method andapparatus for treating multifiber strands of mineral material in amanher to produce a fibrous mass of controlled character in whichtangled clumps or groups of strands are completely eliminated withoutresorting to the use of mechanical pickers or other extraneou devices.

The invention is inclusive of a method of establishing uniform fixationof the adhesive complement in a strand of fibers and of setting upinterflexure or intermovement of the fibers of the strand todisintegrate the adhesive complement to a predetermined controlleddegree so as to subdivide severed strands into smaller strands andliberate or free a portion of the fibers in the severed groups from theremainder of the adhesively joined fibers.

An object of the invention is the provision of a method of directing astrand of bonded mineral fibers in a controlled path wherebyintermovemerit of the fibers in a strand is set up to reduce thecohesion of the individual fibers and of severing the treated strand offibers into comparatively short lengths whereby a controlled mass ofindividual fibers and groups of fibers may be formed, the ratio ofindividual fibers to the integrated groups being controllable throughthe alteration of the path of movement of the strand.

An object of the invention resides in the provision of a method ofcontrolling the opening up of severed strands of mineral fibers throughthe uniform fixation of the adhesive complement in the strand and ofmoving the strand in a manner to cause interfiexure of the fibers in thestrand to fracture or loosen the integrating adhesive or bond holdingfibers in the strand formation so that upon subsequent severing of thestrand to comparatively short lengths, a mass of individual fibers andintegrated groups of fibers may be collocated during collection orintermingled in a controlled ratio.

Another object of the invention is the provision of a method forcontrolling or regulating the density or degree of fiufiiness of a massof severed individual fibers and groups of fibers by establishing andcontrolling relative movement among the fibers of a strand prior to thesevering operation for disintegrating the severed strands to smallerstrands and individual fibers to any predetermined desired extent.

Another object is the provision of method and apparatus for readilyobtaining unopened and partially opened strands for the interior body ofa preform to enhance the strength factor and for obtaining apredominence of discrete fibers for the surface zones of the preform.

Another object of the invention resides in the provision of a method oftreating a strand of glass fibers to fix or harden an adhesivecomplement or coating on the fibers of the strand and direct themovement of the strand in an ogee path to effect a separation or partialseparation of individual fibers in the strand, the extent of flexing ofthe fibers and hence the extent of loosening individual fibers from thestrand being controlled by the character or condition of acuteness ofthe ogee curve traversed by the moving strand.

Further objects and advantages are within the scope of this inventionsuch as relate to the arrangement, operation and function of the relatedelements of the structure, to various details of construction and tocombinati ns 4 parts, elements per se, and to economies of manu factureand numerous other features as will be apparent from a consideration ofthe specification and drawing of a form of the invention, which may bepreferred, in which:

Figure 1 is a semidiagrammatic view of apparatus for carrying out themethod of the invention illustrating the utilization of the cut strandsor fibers in producing fibrous preforms;

Figure 2 is a detail elevational View illustrating a portion of theapparatus shown in Figure 1;

Figure 3 is a side elevational view of the structure illustrated inFigure 2, and

Figure 4 is an elevational view of a combined strand conveying andsevering means usable in carrying out the method of the invention.

The strands of mineral fibers, as for example glass fibers, processed bythe method and apparatus of the present invention may be formed byconventional methods. One method employed includes flowing fine streamsof molten glass from a perforated bushing, attenuating the moltenstreams to comparatively fine continuous fibers and gathering theattenuated fibers into strand or yarn formation. Strands or yarns formedin this manner are economically produced at a high rate of speed.

In order to maintain the attenuated fibers in strand formation tofacilitate handling and processing, it is a usual practice to apply anadhesive, binding or integrating medium to the strand during itsformation. Adhesives such as starch, gelatinous materials, resins 0rbinders capable of hardening are usually applied to the strandconcomitantly with the winding of the strand into a tube, spool orpackage form. Due to the relatively high winding speed of the strand,the adhesive may not be completely "set or hardened on the strand in thecollected package.

After a strand package or tube is thus formed, it is ofttimes storedpreparatory for use in further processing operations. The outermostlayers or convolutions of adhesive-bearing strand being exposed to theair results in the adhesive thereon being substantially set or hardenedwhile the adhesive in the interior of the same package may remain greenor incompletely hardened or may even be in a cohesively plastic or tackycondition. Thus effective control of the extent of subdivision of groupsof fibers or separation of individual fibers from the strands aftersevering is not attainable unless a substantial uniformity of set orhardness of the adhesive or binder on the strand is first attained.

In carrying out the present method of processing strands to form severedstrands of fibers, subdivided strands and individual fibers, referenceis first made to Figure 1 which illustrates a form of apparatus forcarrying out the method. There is provided a frame or creel l0supporting one or more tubes or packages l2 each containing a quantityof continuous strand S formed of attenuated mineral fibers as, forexample, glass fibers. The strand or strands S are directed by means ofguides l4 and i5 through a suitable oven 16 or other means for eifectinga uniformity of hardness or set of the adhesive or binder on the fibersof the strand. As illustrated, the oven [6 through which the strands Sare conveyed may include one or more series of heating devices I 8 inthe form of electrically energized heat lamps or jets of burningcombustible mixture for establishing a zone of elevated temperature tofix or harden the adhesive. If desired, for certain types of adhesivethat may be readily air dried, the heating devices may be supplementedwith a current of air passing through the adhesive hardening oven.

By this or an equivalent means the adhesive or binder on the strandleaving the oven I6 is conditioned to a uniform hardness so that aneffective control of the opening up or separation of individual fibersor groups of fibers from the strands may be attained. The strands S aredirected into engagement with a strand conditioning means 2|]hereinafter explained in detail from whence the strands move to asevering means 22. The use of the oven may be dispensed with if thepackages or spools of strand are stored or treated at room or elevatedtemperature for a sufiicient period to attain a desired and uniformdegree of set or cure of the adhesive or bindin agent.

The strand severing means 22 is inclusive of a strand conveying ortensioning means for withdrawing the strands from the supply packages orspools l2, moving same'through the oven It to the strand conditioner 2cand thence to the strand severing device. The strand severing meansillustrated and particularly shown in Figure 4 is inclusive of a strandconveying roll 25 which is provided with a resilient exteriorcylindrical surface formed as a sleeve 28 of yieldable or resilientmaterial, as for example, rubber or the like. The strand conveying roll25 is preferably mounted in bearings 28 carried in a suitablesupplemental frame 29 which is mounted upon a main frame 30, the frame29 being adjustable relative to the fram 30 by means of an adjustingmeans or screw 32.

Disposed above the strand conveying roll 25 is a roll 34 having a shaft35 disposed in slots 36 formed in guides 31, the latter being slidab-lyengageable with the bifurcated portion of the frame 29, only one Of theguid members 31 being illustrated. The roll 34, which is preferably inthe form of a solid metal cylinder is adapted to be superposed againstthe strand or strands S to urge the same into frictional engagement withthe strand conveying means or roll 25. The roll 34 is mounted in amanner whereby it is freely movable in a direction parallel with thebifurcated portion of th frame 29 so that the weight of the roll 34 isat all times effective to hold the strands in engagement with theconveyor 25.

The severing means for the strands is inclusive of a cylindrical roll ormember 49, the shaft 4! of which is mounted in bearings 42 supportedupon the main frame 343. The roll is provided with strand severing barsor knives 44 which are spaced at predetermined peripheral distances onthe roll 40 equal to the length or lengths desired for the severedstrands. The cylinder 49 is preferably formed of metal and the knives 64are held in grooves or slots formed in the roll 40 by means of collarsarranged at the ends of the roll.

The severing knives or bars 4% project outwardly of the peripheralsurface of roll 40 a distance sufiicient to sever the strands S with thecutting edges of the knives contacting and slightly depressing theresilient or rubber surface of the conveying roll 25. The position ofthe latter may be adjusted by the adjusting means32 so as to insure astrand severing action between the knives M and the strand conveyingroll 25.

The strand conveyor roll 25 and the knife carrying roll 40 aresimultaneously driven by a strand to control the extent ofdisintegration means of gearing (not shown) and a belt 43 connected to amotor (not shown) whereby the strand severing knives 44 move at a linearspeed substantially equal to that of the strand conveying roll 25 sothat there is no appreciable relative movement between the strands S andthe roll 40. Thus the severing of the strands is effected by meanstraveling at substantially the same linear speed as the strands.

The severed strands and fibers may be collected in any desired mannerdependent upon the particular purpose for which the severed materialsare to be used. As illustrated in Figure 1, the cut strands and fibersmay be immediately utilized to produce fibrous preforms through the useof a suitable apparatus hereinafter further described. If a uniplanarfibrous mat is to be formed, the cut strands and fibers may b collectedupon a suitable foraminous conveyor and a suitable binder or adhesiveapplied to insure mass integrity in the mat. The out strands and fibersmay be transferred to a station remote from the severing zone forfurther processing or use through the employment of a moving air streamor other conveying or transferring medium.

As has been previously stated herein, it is highly desirable to effect adisintegration of the severed strands to separate individual fibers,groups of fibers or a combination thereof depending upon the purpose forwhich the collected fibrous mass is to be used. For example, in sometypes of preform construction incorporated as reinforcement intranslucent or light transmitting resins or plastics, th appearance ofthe molded article is enhanced through the presence of a predominateratio of individual fibers at the surface of the reinforcin preform withthe high strength groups of fibers in the interior.

Another advantage of separating individual fibers from severed strandslies in economy of the amount of glass in a mat or preform where therequired. strength factor may be adequately supplied by relatively fewunopened or partially opened severed strands of fibers. The fiuffiness,resiliency and density of the mat 0r preform may be accuratelycontrolled by regulating the ratio of unopened strands, partially openedstrands and separated fibers in the mass.

The apparatus for accomplishing this control is inclusive of a means forfracturing or partially fracturing the adhesive or integrity formingmedium in the fibers of a strand in a manner whereby upon severing ofthe strands, individual fibers and groups of fibers are separatedtherefrom. The apparatus involves an adjustable mechanism for regulatinor controlling the extent of fracturing or reducing the bondingefi'ectiveness of the integrity factor in the fibers of of the severedstrands.

The method of accomplishing this result involves an alteration or changein the direction of movement of a strand while the latter is in a stateof tension to set up or establish intermotion or relative movement orflexure among the fibers or certain of the fibers of the strand toreduce the integrity factor or fracture the adhesive joining the fibersin strand formation.

One form of means for accomplishing this purpose is illustrated inFigures 1 and 2 being in the nature of a snubbing device which isinclusive of a support or frame member 50 upon which is movably mountedan arm or element 5!. The

element and support 50 are formed with registering openings adapted toreceive a threaded bolt 53 upon which is threaded ,a wing nut 55 orother suitable securing means. The arm 5| carries a pair of spaced pinsor rods 56 adapted to be engaged by the strands S prior to theirmovement to the severing zone.

The strands S traverse a path around the pins 56 in generalconfiguration of an ogee curve, one adjustment of the member 5| forcausing such traverse of the strands being illustrated in Figure 1. Thearm 5| may be provided with an extension 56 carrying a bolt 59 adaptedfor traverse in a slot at of a member 6!, the latter being secured tothe frame 59. The bolt 59 is provided with a wing nut 62 for tighteningthe extension 58 of arm 5| into fixed engagement with the member 6| soas to provide adequate means for retaining the arm 5| in adjustedposition supplementing the securing means 54.

It is to be understood that other equivalent means may be utilized tosecure arm El and pins 56 in adjusted position without departing fromthe spirit of the invention. The member 6| may if desired be providedwith graduations 63 arranged for cooperation with the arm extension 58to accurately position or determine the relative adjustment of the army5| and pins 56.

By adjusting the relative angularity of the direction of travel of thestrand between pins 5|? with that of the strand approaching and leavingthe snubbing device, designated as angles A in Figure 1, the acutenessor sharpness thereof controls the amount of relative intermovement andflexure of the fibers and the extent of fracturing the binder on thefibers. The extent of fracturing or loosening of the binder determinesthe relative proportions of severed unopened strands, strands containingfewer fibers and independent fibers resulting from the severingoperation.

Through adjustment of the plate 5| so that angles A are made larger orsmaller, the fluid-- ness of the mass of severed strands and fibers isrespectively reduced or increased. It has been found that when angles Aare of the order of fifteen to thirty degrees, the resulting cut strandsseparate into individual fibers to a large extent whereby the mat,preform or other product made therefrom is very fluffy in nature and oflow density.

If the plate 5| is adjusted so that the angles are quite largeapproaching an obtuse character in the order of one hundred and twentydegrees, the major number of severed strands remain integral andseparate into smaller strands and into individual fibers only to alimited extent whereby the resulting product is of comparatively highdensity and lacks flufiiness. Various adjustments of the plate 5i may bemade dependent on the character of cut strand and fiber proportionsdesired, the degree of hardness of the binding agent, the type andcharacter of the binding agent, the size and number of fibers making upthe strands and the linear speed at which the strands are drawn throughthe snubbing or strand fiexing instrumentality.

As the method and apparatus of the invention are especially suited forthe economical produc tion or formation of fibrous preforms asreinforcement for articles molded of resin or plastic, 8.semidiagrammatic view of a type of apparatus for fabricating preforms isillustrated in Figure l. The arrangement is inclusive of a frame 68supporting a plenum chamber 10 provided with an inlet or entrance 12 forthe admission of cut strands and fibers directly from the strand severing device 22. Disposed at a lower Wall of the plenum chamber is aplaten I3 adapted to support a foraminous matrix 74 upon which the cutstrands and fibers are deposited or collected to produce a preformconfiguration 15. The platen is preferably angularly disposed and isrelatively movable to facilitate uniform distribution of the fibrousmaterial on the matrix. The platen i3 is secured to a shaft 17 and abushing 18, the shaft being journaled for rotation in a bearing means3!] carried by the frame. The shaft TI is driven by reduction gearing 82which in turn is connected by a belt and pulley assembly 83 with a speedchanging mechanism contained within a housing 85. The speed changingmechanism is driven by an electric motor 86. A control of the speed ofrotation of the matrix M, platen i3 and shaft 11 is effected throughregulation of the speed changing mechanism by means of a control handleor member 88. The cut fibers and strands are entrained in an air streamas they leave the severing zone and are carried to the matrix 14. In theembodiment illustrated, the air stream is provided by a blower orsuction producing device 90, the rotor thereof being driven by means ofa pulley and belt arrangement 92 from an electrode motor 93. Under theinfluence of the suction producing device 93 which exhausts through duct94, air is admitted through the entrance 12 of the plenum chambercarrying the cut fibers and strands to the matrix it where they arefiltered from the air stream and build up into a fluffy preform 15.

It is to be understood that the severing means 22 may be remotelydisposed with respect to the preform producing device and the air streamor other suitable conveying means utilized to transfer the cut strandsand fibers to the plenum chamber 10.

The method and apparatus is especially suited to vary the proportions ofstrand groups and individual fibers in an accumulated mass duringcollection of the cut strands and fibers to modify the proportions invarious zones of the product. For example, a surface lamina of a mat orpreform may be formed substantially entirely of individual or separatedout fibers by adjustment of plate 5| to render the angles A extremelyacute, and by making angles A less acute, a succeedin lamina in theproduct may be formed with un opened severed strands or smaller strandgroups.

The snubbing instrumentality may be arranged to be automatically shiftedby suitable means during the formation of a preform whereby initiallythe cut strands are fully opened to provide discrete fibers, theinstrumentality being then shifted to a position to produce unopened orintact cut strands and subsequently moved to a position to again producefully opened strands or discrete fibers to thereby impart a smoothfinish on both surfaces of a molded resinous article embodying thereinforcing preform.

Thus the method and apparatus provides for a broad range in Variation ofthe character of the fibrous product yet with precision controlexercised at all times. Furthermore, due to the fact that the bindingagent on the fibers is cornpletely dried or hardened, the fibrousproduct contains no tangled clumps or cohering groups of severed strandsthus assuring uniform char acter of the product.

It is apparent that, within the scope of the invention, modificationsand different arrangements may be made other than is herein disclosed,

and the present disclosure is illustrative merely,

the invention comprehending all variations there- I claim:

1. A method of conditioning a continuous strand of mineral fibersincluding feeding an adhesive-bearing strand in a rectilinear direction,of engaging the strand with an instrumentality for altering thedirection of movement thereof to loosen the adhesive on the fibers, andof controlling the extent of change in the direction of the movingstrand for regulating the extent of loosening of the fibers in thestrand.

2. A method of conditioning a continuous strand of bonded mineral fibersincludingfeeding the strand to a bond fracturing instrumentality forloosening fibers of the strand, and of modifying the bond fracturingeffectiveness of the instrumentality for regulating the extent oflooseness of the fibers in the strand.

3. A method of conditioning a continuous strand of bonded mineral fibersincluding feeding the strand to a bond fracturing instrumentality forloosening fibers of the strand; and of modifying the bond fracturingeffectiveness of the instrumentality for regulating the release of thefibers in the strand, and of conveying the strand from the bondfracturing instrumentality to a strand severing zone, and of severingthe strand into comparatively short lengths whereby a mass of groups ofsevered fibers and individual fibers is produced.

4. A method of conditioning a continuous strand of mineral fibers, oftreating the strand with an integrating medium to establishinteradhesion among the fibers in the strand, of treating theintegrating medium in the strand to establish substantially uniformfiber integrity; of engaging the strand with an instrumentality formodifying the effectiveness of the integrating medium to effect aloosening of the fibers, and of modifying the operative relation of thestrand with the instrumentality to control the extent of loosening ofthe fibers in the strand.

5. A method of conditioning continuous strands of mineral fibers whichincludes the steps of applying an adhesive to a strand of fibers; oftreating the adhesive constituent in the strand to secure substantiallyuniform fiber integrity in the strand; of moving the strand in atortuous path to set up relative intermovement among the fibers of thestrand to loosen fibers in the strand, and of reducing the strand topredetermined comparatively short lengths whereby some of the reducedstrands are subdivided into smaller strands and separated fibers.

6. A method of conditioning continuous strands of attenuated glassfibers which includes the steps of applying an adhesive to the fibers ofthe strand; of treating the adhesive constituent of the strand to securea substantially uniform hardness; of moving the strand in a tortuouspath to set up relative intermovement among the fibers of the strand toreduce the bonding effectiveness of the adhesive; and of varying thecharacter of the tortuous path of the strand for controlling thereduction of bonding efiectiveness of the adhesive.

7. A method of conditioning continuous strands of attenuated glassfibers which includes the steps of applying a bonding agent to thefibers of the strand; of treating the bonding agent in the strand tosecure substantially uniform fiber integrity; of moving the strand in acontrolled tortuous path to set up relative intermovement among thefibers of the strand to loosen fibers in the strand, and of reducing thestrand to predetermined comparative short lengths to provide a mass offibers the density of which is determined by the character of thetortuous path traversed by the strand.

8. A method of treating a continuous strand of adhesive-bearing mineralfibers including the steps of subjecting the strand to an adhesivehardening treatment; of directing the treated strand to a fiberloosening station; of flexing the strand at the fiber loosening stationfor dislodging the adhesive; of controlling the character of strandfiexure for regulating the extent of dislodgment of the adhesive, and ofsevering the flexed strand into lengths whereby a controlled mass ofshort length strands, divided strands and separated fibers is produced.

9. A method of treating a continuous strand of adhesive-bearing mineralfibers including the steps of subjecting the strand to an adhesivehardening treatment; of directing the treated strand in a tortuous pathto flex the fibers of the strand for dislodging the adhesive; ofcontrolling the character of the tortuous path of the strand forregulating the extent of fiber flexure and dislodgment of the adhesive,and of severing the flexed strand whereby comparatively short lengthseparated fibers and groups of adhesively joined fibers are produced.

10. A method of processing a continuous strand of mineral fibers bearinga fiber integrating medium including the steps of subjecting the strandto an integrating medium fixation treatment; of moving the treatedstrand to a strand flexing station; of flexing the fibers of the strandto reduce the interfiber bonding effectiveness of the integratingmedium; of controlling the extent of fiexure of the fibers at the strandflexing station for regulating the extent of reduction of interfiberbond, and of severing the flexed strand into predetermined comparativelyshort lengths to form a flufiy mass, the density of the mass beingdependent upon the extent of reduction in interfiber bondingeffectiveness of the fiber integrating medium.

11. A method of processing a continuous strand of mineral fibers bearinga fiber integrating medium including the steps of subjecting the strandto an integrating medium fixation treatment; of moving the treatedstrand to a strand flexing station; of flexing the fibers of the strandto reduce the interfiber bonding effectiveness of the integratingmedium; of controlling the extent of fiexure of the fibers at the strandflexing station for regulating the extent of reduction of interfiberbond, and of severing the flexed strand into predetermined comparativelyshort lengths to produce a mixture of individual fibers and groups ofinterbonded fibers.

12. A method of producing a mat of mineral fibers including the steps ofconveying a continuous linear group of mineral fibers bearing aninterfiber bonding material to a fiber flexing zone; of directing thegroup of fibers in a tortuous path in the flexing zone to establishrelative movement of some of the fibers in the group to reduce theefiectiveness of the interfiber bond; of severing the flexed group offibers to comparatively short lengths; of collecting the severed lengthsto form a fibrous mass, and of controlling the character of the tortuouspath and the eiiectiveness of the interfiber bond for varying thedensity of the collected mass of fibers.

13. A method of producing a mat of attenuated glass fibers including thesteps of conveying a continuous linear group of fibers bearing aninterfiber bonding material to a fiber flexing zone; of directing thegroup of fibers into engagement with a fiber flexing instrumentality toestablish relative movement of some of the fibers relative to others toreduce the effectiveness of the interfiber bond; of severing the groupof flexed fibers to predetermined short lengths; of collecting thesevered lengths to form a mat composed of a mass of individual fibersand bonded groups of fibers; and of controlling the efiectiveness of thefiber flexing instrumentality to fracture the interfiber bond forvarying the density of the collected mass of severed fibers.

14. A method of controlling the density of a collected mass ofindividual fibers and bonded groups of fibers produced fromfiber-forming mineral material including moving a continuous lineargroup of bonded fibers to a fiber flexing zone; of flexing the lineargroup in a manner to cause relative intermovement of some of the fibersand a fracturing. of the bond on some of the fibers; of reducing theflexed group to comparatively short lengths and. collecting them into amass; and of regulating the character of flexure of the linear group tovary the ratio of individ ual fibers to bonded groups of fibers in thecollected mass for establishing a predetermined den sity for the mass. v

V HAROLD W. ESSMAN.

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